1. Field of the Invention
The field of this invention is the separation of heavy non-magnetic materials from a fluid body, especially as applied to dentistry.
2. Information
In dental offices the grinding and polishing of teeth produces small bits of gold, dental amalgam, and/or other waste materials which are then inputted by a vacuum process into a waste water system. Dental amalgam contains mercury, which is environmentally hazardous. Disposing of the waste water containing the mercury into a municipal sewer system is no longer acceptable in many locales, especially where it is prohibited by law. Reliable separation of the mercury, whether with or without the accompanying waste water, needs to be accomplished so that the mercury can be recovered or else disposed of as hazardous material.
Gold has advantages for dentistry which have long been known. Gold is non-magnetic and has a density of 19.
The so-called silver fillings used in dentistry are more accurately described as amalgam, and are typically made of a mixture of silver and mercury. Silver is non-magnetic and has a density of 10.5. Mercury is non-magnetic and has a density of 13.
When mercury, a liquid metal, is physically mixed with certain other metals it attempts to alloy with them. This reaction between mercury and base metals is called amalgamation, and is a property peculiar to mercury alone. Mercury is able to amalgamate with silver as well as with some other base metals.
Dental amalgam often contains mercury (45 to 50 percent), mixed with an alloy of silver, tin, and copper (50 to 55 percent). Mixing of the silver filling materials is a dangerous process which must be carefully monitored in the dental office. When those materials are first mixed together, and even before the silver filling is placed into the patient's tooth, the materials begin to form an amalgam and to harden. The amalgam is also non-magnetic and typically has a density of about 12.
In dental offices the waste materials derived from a patient's mouth are applied along with waste water to a screen cup that will remove large objects including amalgam. The screen cup may from time to time be removed and replaced at will. The screen cup generally captures a very large portion of the amalgam and other bulky materials.
The dentist and his or her assistants must carefully monitor their working time and utilize it very efficiently. In disposing of a hazardous chemical material it is important to minimize the possibility of error. It is therefore desirable to avoid or minimize procedures that rely upon office staff. A waste disposal process should preferably operate by itself automatically, without the need for any attention by the office staff.
When bits of amalgam enter the dental waste water they do not automatically divide themselves into the individual components from which they were formed. The complete separation of the mercury from silver, silver alloy, and/or other constituents of the amalgam, may require a combination of mechanical, temperature, and/or chemical process steps.
Some bacteria in municipal waste systems are capable of converting the free mercury found in dental amalgam into the organo-mercuric compound methyl mercury. This form of mercury is responsible for birth defects and nervous disorders in people exposed to methyl mercury through their food. That is the reason why disposing of mercury-containing amalgam into a municipal sewer system is no longer considered acceptable. Recovery of the amalgam and mercury at the point of generation is greatly preferable.
The vacuum process used in dental offices starts at the patient's mouth. Water carrying the waste materials is removed by a vacuum system. The vacuum system at its output end generates an intermittent and very forceful water stream, including widely varying amounts of water, dental waste, and air.
Disposal of waste materials collected from dental waste liquid or fluid is typically performed by an outside contractor to whom the task of separating out and recovering the mercury is delegated. The gold and silver contained in the dental waste water can then be refined to provide an economic return for reducing the charges of the disposal contractor. But whether or not the gold and/or silver is refined and reclaimed, it is very important and apparently quite necessary to have a reliable and safe method for recovering the mercury and disposing of it other than to a public sewer.
There are therefore two very important objectives for a dental amalgam disposal system. One important objective is to remove at least a large percentage of the amalgam from the dental waste water or effluent. For that there is an ISO standard prescribed by the International Standards Association. A second and separate important objective is to protect the waste water entering a public sewer system from excessive mercury levels. The Environmental Protection Agency (EPA) is reported to have reduced the level of mercury that is permissible in waste water dumped into the Great Lakes to only twelve parts per trillion. That standard would present a great challenge to the dental profession for the appropriate handling of amalgam disposal.
An article entitled “Purchasing, installing, and operating dental amalgam separators” published in the Journal of the American Dental Association, Vol. 134, August 2003, at Pages 1054 and following, described practices then recommended to the profession for handling and disposing of amalgam.
Centrifugal Concentrators. It has long been known to use centrifugal separators for separating amalgam from dental office waste water. Such separators are efficient for separating out large objects that also have a high specific density. They are limited, however, in their ability to separate out very small objects. Thus, passing the waste water through a succession of centrifugal separators would remove a great deal of material in the first separator, but much less in the second, and probably very little in the third.
Sedimentation systems. An example is the sedimentation system sold under trademark “The AMALGAM COLLECTOR” by R & D Services, Inc. of Seattle, Wash. 98103. In that type of separator the water does not flow continuously through, but instead is captured in the settling chamber. For a small dental office the sedimentation chamber might be large enough to hold all of the waste water generated during one working day. To provide space for the further inflow of waste water the office staff would then need to carefully draw off the excess water, while also avoiding any disturbance of the accumulated heavy waste or sludge. Settling or sedimentation occurs slowly over time, so the drawing off of excess water would normally be done the first thing in the morning after an overnight settling period. Excess water is then often dumped into the sewer system even though its amalgam and mercury content might greatly exceed a recommended safe level. At appropriate times the remaining sludge containing the captured amalgam will be emptied from the container and taken to a refinery or recovery process. Staff persons who are unskilled in the use of the sedimentation equipment may very well make mistakes leading to inadvertent loss of mercury into the public sewer.
Chemical Separation. It is also known to use ionization processes and adsorbent materials to remove amalgam and mercury from the dental waste water. An example is described in U.S. Pat. No. 7,063,793 issued Jun. 20, 2006. Those procedures require a continuous electrical energy supply for their reliable operation, and may also require additional water to be added as a supplement to the normal inflow of dental waste water. Because of the required staff attention this kind of procedure is also subject to a significant possibility of error.